超大城市新粒子生成事件对云凝结核贡献分析

Contribution of new particle formation to cloud condensation nuclei in megacities of China

高浓度气溶胶在受人类活动影响的污染地区种类和组成非常复杂,因此,其环境和气候效应引起了广泛关注,但在超大城市背景下气溶胶粒子活化成为云凝结核的过程与边界层的相互作用尚不完全清楚.本研究基于北京(BJ)、上海(SH)、广州(GZ)的观测数据,选取3个城市的春季和冬季(北京冬季11月和广州冬季12月的连续观测,以及上海春季4月的加强观测)集成观测气溶胶数据和云凝结核同期观测的变化并结合其他污染物演化规律,对比分析了新粒子生成事件和环境变量演化对3个超大城市云凝结浓度形成的影响.结果表明,以用云凝结核(CCN)浓度与气溶胶(CN)数浓度的比值作为3个城市的活化率,北京CCN数浓度约为(500±200)#·cm^(-3),CN最大浓度小于(1.0×10^(4)±0.3×10^(4))#·cm^(-3),活化率约为0.07%.上海CCN数浓度为(1500±500)#·cm^(-3),CN最大浓度小于(98.0×10^(4)±0.3×10^(4))#·cm^(-3),最大活化率为0.05%.广州CCN数浓度为(150±30)#·cm^(-3),CN最大浓度为(24.0×10^(3)±0.3×10^(3))#·cm^(-3),最大活化率为0.03%.本文旨在阐明气溶胶物理化学性质(粒子谱、化学成分、排放源等的时空演变特征)在不同排放源和大气边界层条件的影响下,造成不同类型的排放和输送过程对气溶胶活化率的影响,对比发现新粒子生成(NPF)期间CCN数浓度明显高于非新粒子生成(Non-NPF)时期,证明NPF发生时对CCN的活化率(AR)有显著的提升,在过饱和度SS=0.1%下,北京达到峰值在4×10^(-3)附近,广州的最大值约为17×10^(-4),上海的最大值为3×10^(-3).且在NPF期间气溶胶活化率显著增加,3个超大城市在NPF和Non-NPF期间,CCN数浓度与活化率的关系在上海尤其明显,化学成分包括有机物、硝酸盐和硫酸盐等物质也会影响超大城市地区气溶胶粒子的活化率,对比发现3个城市在NPF期间CCN数浓度和活化率都明显区别于其他时段.发现气溶胶的物理和化学性质以及与活化率的直接关系,可用以评估新粒子生成对区域大气环境(如霾)的影响,并估计气溶胶贡献为CCN的间接气候影响.

High concentration of aerosols in polluted areas has complex composition affected by human activities.The environmental and climate effects of these aerosol particles have attracted extensive attention but the interaction with the atmospheric boundary layer is not clear.Based on the intensity observation from Beijing,Shanghai and Guangzhou(hereinafter referred to as BJ,SH and GZ),we analyzed the influence of the aerosol variation of number concentration(CN)on cloud condensation nuclei(CCN)in different seasons(mainly in spring and winter)in three cities,namely BJ in November 2016,GZ in December 2019 and SH in April 2020.Among the three megacities,the concentration of CCN in BJ is about(500±200)#·cm^(-3),the peak concentration of CN is less than 1×10^(4)#·cm^(-3),the activation ratio is about 0.07.The concentration of CCN in SH is(1500±500)#·cm^(-3),the maximum concentration of CN is less than 98×10^(4)#·cm^(-3),and the maximum activation ratio was less than 0.02~0.05.The concentration of CCN in GZ is in the range of(150±30)#·cm^(-3),and the peak concentration of CN is less than 24×10^(3)#·cm^(-3),the maximum activation ratio is less than 0.03.This paper clarified the contribution of spatiotemporal evolution characteristics of physical and chemical properties of aerosols(including particle size distribution,environment characteristics,emission source,etc.)to CCN under the influence of different emission sources and atmospheric conditions.We found the physical and chemical properties of aerosols play an important role in evaluating their impact on regional atmospheric transport(such as haze)and estimating the indirect effects of aerosols on CCN and climate.